There is the tutorial on the wiki. But I'll tell you my method (which is on the wiki ...)
First, start you level. The level or you take a "photo" which will be display in the level select. Of course, we'll see Sonic on it ! So, we open the console with ².
Tape the 3 following commands, and then tap entry.
Chasecam 0
==> This command will show the level as if you were Sonic.
showhud off
==> This command will remove your lives, your rings, time, score, etc..of the screen.
crosshair off
==> This command will remove the little cross which will be displayed in the middle of the screen, when you will put showhud off and Chasecam 0 in the console.
After that, you will see THAT THE LEVEL.
Find a nice place for your level, and take a picture (a screen) with F8. I advise you to take several pictures with F8, the first is never the best.
The photos are stored in your SRB2 folder.
Then, you must adjust the photos to have the size 160x100.
Me, I use Irfanview software, and I will advise:
Download link:
http://dw.com.com/redir?edId=3&siteId=4&oId=3000-2192_4-10021962&ontId=2192_4&spi=e8e3ee727ea4b326a8f679bb8a10f405&lop=link&tag=tdw_dltext<ype=dl_dlnow&pid=11381191&mfgId=59333&merId=59333&pguid=Ni9fkwoPjAEAAF7LhNwAAAAC&destUrl=http%3A%2F%2Fdownload.cnet.com%2F3001-2192_4-10021962.html%3Fspi%3De8e3ee727ea4b326a8f679bb8a10f405%26part%3Ddl-IrfanView
Well, once installed, launch it. Its icon is a kind of red cat.
Open the file srb20000 with Irfanview.. that is in your SRB2 folder. Take the best picture of the level, one that you like and that will be in the Level select.
Once open, do the keyboard combination CTRL + R.
You'll see a small window appear. Somewhere in this window is the size of your image, two little white blocks with numbers in it (The size must be 340x200, something like that, but NEVER below 100x100, totally impossible ...)
You must replace by the size 160x100 and select OK.
Save your image on your desktop, or there or you want.
Now, add the file in the wad!
Open your wad with XWE or Slumped.
How to save the image if you use XWE:
We must create the image lump.
So, go ENTRY => NEW.
For the name, you must type MAPXXP
XX represents the number of your map. For example, if your card is the first, so she replaces Green Flower Zone 1, you must call the MAP01P.
Put the P in the end, huh !
Click OK.
Then, import the image into the lump. So right-click on MAPXXP, and "Replace Entry".
You select the image format 160x100.
The image is already converted to DOOM, it works. Save, and normally it works! Tell me if there is a problem.
How to save the image if you use Slumped:
We must create the image lump.
So go LUMP => NEW.
For the name, you must type MAPXXP
XX represents the number of your map. For example, if your card is the first, so she replaces Green Flower Zone 1, you must call the MAP01P.
Put the P in the end , huh !
Click OK.
Then, doing a right click on your lump MAPXXP, and select "Import".
Select the image converted to 160x100 to your level.
Then again right click on MAPXXP, but this time chose CONVERT TO => GFX DOOM.
The image is ready. Save your wad, and tests, it should work.
Hope to have you help.